In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, dust particles, sometimes referred to as fly ash. The dust particles are often removed from the process gas by means of an electrostatic precipitator, also called ESP, for instance of the type illustrated in U.S. Pat. No. 4,502,872.
A combustion plant normally comprises a boiler in which the heat of the hot process gas is utilized for generating steam. The operating conditions of the boiler may vary from time to time depending on the degree of fouling on the heat transfer surfaces, the type and amount of fuel supplied, etc. The varying conditions in the boiler will cause varying conditions of the process gas that leaves the boiler and enters the ESP. The U.S. Pat. No. 4,624,685 describes an attempt to account for the varying process gas conditions in the control of an ESP. The flue gas temperature is accounted for as it has been found, in accordance with U.S. Pat. No. 4,624,685, that a higher temperature will result in a higher volumetric flow, the power of the ESP being controlled in accordance with the measured temperature to account for the varying volumetric flow of the process gas. Hence, an increased flue gas temperature is considered as corresponding to an increased volumetric flow requiring an increased power to the ESP.
Operating an ESP in accordance with U.S. Pat. No. 4,624,685 may be successful in the sense that emission limits can be coped with at varying conditions of the process gas. However, the electrical strain on the electrical components of the ESP tends to be quite high.